The present invention relates generally to wideband television tuners for signals in the VHF, CATV and UHF bands.
In a known wideband tuner for reception of television signals in the VHF, CATV and UHF bands as shown and described in Japanese Patent No. 53-38129, the CATV and UHF tuning sections are cascaded so that CATV signals are coupled to the CATV tuning section and converted into a UHF frequency and fed to the UHF tuning section for further frequency conversion to the standard video intermediate frequency, while UHF signals are coupled direct to the UHF section for conversion to the standard intermediate frequency. The CATV tuning section includes a local oscillator which supplies a carrier at a frequency lower than the frequency of the received CATV signal to a summing type mixer so that the output of the mixer is at a frequency which is a sum of frequencies of the carrier and the received signal, a modulation technique known as "a lower-side band summing mode". However, with this type of modulation an appreciable amount of spurious signals arising from the modulation falls in the bandwidth of the converted intermediate frequency signal. Other difficulties involved with the prior art tuner are poor selectivty, low sensitivity and high leakage current at the input to the CATV tuning section during UHF reception mode. In addition, the prior art tuner is complex in circuit design which can result in costly equipment.